This application is based upon application No. 2000-252347 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a device having a unit, which can be attached to or removed from a body of the device, such as a camera having an interchangeable lens, and relates to a method for controlling the unit from the body of the device. More specifically, the present invention relates to an equipment in the device for driving a driven member in the unit by means of a driving source provided in the body, and relates to the method for controlling the driven member from the equipment.
2. Description of the Related Arts
Conventionally, there have been proposed some camera systems, in which an aperture in a lens is driven by a camera.
For example, as for a camera provided with a motor, Japanese Non-examined Patent Publication No. 58-224336 discloses a technique that realizes non-provision of the urging means for resetting an aperture device in a lens, by making use of charging operation which makes the aperture device execute its resetting operation. It is disclosed therein that the aperture device is driven by a motor in a camera and stopped by a magnetic mechanism, and that a ring for driving the aperture device is urged in one direction in a connecting part between the camera body and the lens.
In U.S. Pat. No. 4,681,417, it discloses a technique that a small and low power motor only for actuating an aperture device in an interchangeable lens is equipped in a camera body. It is disclosed therein that a linear driving lever in the camera body and an aperture driving lever in the lens are provided for connecting parts between the body and the lens, and that its stopping position of the aperture device is detected by the lens.
In Japanese Non-examined Patent Publication No. 8-95145, it discloses a technique of lens changeable camera disposed at predetermined positions in a lens mount portion, in which an aperture driving mechanism and a focus driving mechanism are connected with two pairs of couplers, each having a key at a tip thereof. Engagement in a connecting portion is realized by at least one revolution (or rotation) of the couplers, and it is not necessary to align a mechanism of an interchangeable lens. Thus, the technique is suitable for an aperture driving system without urging springs, but retreating mechanism and the like are needed in order to disengage it from the connecting portion.
As for a driving mechanism driven and stopped by a motor, an overrun is necessarily occurred from a point of starting brake to a point of stopping. Main reasons of the overrun are stopping characteristics of the motor or a driving source, construction of the driving mechanism such as gear ratio and transfer property, load or inertia of driven members and so on.
As for control, the technique that driving operation started a little earlier (or ahead of time) in consideration of the delay of control system, is known.
For example, in U.S. Pat. No. 4,396,271, it is disclosed that calculating of moving distance of a movable aperture member, and starting to stop an aperture device when the aperture member arrives at calculated distance short of an object position (or target position) corresponding to aperture value, allow for precise aperture control.
In U.S. Pat. No. 4,538,893, a driving mechanism for changing the size of an aperture, driven through an aperture associated member by a motor, is disclosed. In the driving system, the displacement amount of the aperture associated member is detected; a position signal and a rate signal are produced; and the aperture associated member is controlled to stop at an object position, by means of correcting the position signal responding to the rate signal.
As for common methods for predicting overrun of a motor by velocity detected before braking, it is disclosed, for example, in U.S. Pat. No. 5,543,878, that a film feeding apparatus, comprising a decelerating controller for decelerating film feeding velocity, a reverse drive brake for stopping to feed a film by reversing the motor, a velocity detector for detecting the film feeding velocity, and a brake controller for controlling the decelerating controller and the reverse drive brake. In this apparatus, the fluctuation in the rate of reducing the speed, namely deceleration, depending on some conditions, causes errors.
In U.S. Pat. No. 4,745,425, it is disclosed that a lens barrel having a optical system adjusting to focus automatically responding to a signal detected by a focus detect means, is provided with a storing means for storing information about load torque in the optical system, such as data about load and inertia, in order to change the condition of adjusting the optical system during automatic focusing. In the lens barrel, it is difficult to employ a lens having no data, and to correspond to every lens with individual difference, including change in characteristics accompanying aging.
In Japanese Non-examined Patent Publication No. 7-181573, a method for controlling a motor in a camera is disclosed. According to this method, the motor is controlled responding to a signal, corresponding to a revolution of the motor, output by an encoder, and a film is stopped at an object position, by means of adjusting the velocity of the motor so as to follow a brake line indicating a function of operation start point, which is predetermined, and the velocity of the motor. This stopping control tasks a controller, and therefor the controller, is too busy to perform the other controlling operation at one time.
In an inexpensive camera system using an interchangeable lens provided with no motor, a motor built in a camera body drives an aperture device in the lens, and a long link mechanism from the motor to a driven member of the aperture device is needed. In that system, a spring for urging an aperture control member is needed in order to prevent play in the long link mechanism and stabilize stopping characteristics thereof. The spring can be provided in the camera body or in the interchangeable lens. In case that the spring is not provided in the interchangeable lens, connecting members, provided in the interchangeable lens, for connecting between the camera body and the interchangeable lens are unsteady, and therefor an engaging member provided in the camera body needs to dodge connecting members when attaching the lens to the camera body. On the contrary, in case that the spring is provided in the interchangeable lens, one-way urging mechanism can be provided in the camera body, and connecting mechanism between the camera body and the interchangeable lens can be simplified.
In case that a DC motor in a camera body drives a mechanism including spring urging mechanism in a interchangeable lens, it is possible to drive it in both directions by means of supplying the DC motor with electricity, but it is difficult to keep it stopping against urging of the spring without supplying the DC motor therewith. Specifically, the DC motor has a small static force, consisting of magnetic cocking and frictional force, and therefore, a reduction ratio of a transfer mechanism must be large enough to keep stopping against the spring force only by means of the static force.
In case that the DC motor having a small inertia is used in order to shorten aperture drive time, cocking torque diminishes and therefor, the reduction ratio needs to be enlarged much more.
In case that a stepping motor is provided in a camera body, it is possible to keep stopping against spring force by means of continuing to supply the same magnetic poles of the motor with electricity, but the reduction ratio needs also to be enlarged because the torque produced by the stepping motor is usually small.
High reduction ratio enough to keep stopping against the spring force only by means of stopping the motor causes a problem of prolonging stop down operation time, because revolutions of a output axis of the motor for stopping down in a set amount increases. Stop down operation time is one of causes influencing release time lag, which is a delay time from a point of pushing a release button to actual exposure. Thus, it is desirable that stop down operation time is as short as possible.
Moreover, in case that a motor is provided not in an interchangeable lens but in a camera body, and that the motor is driven in both directions in order to continue to actuate the aperture device, conflicting problems are caused. One is operating time, and the other is accuracy of stopping position.
Specifically, in case that a reduction gear ratio from the motor in the camera body to an aperture device in the lens is made as small as possible while preventing the operation time from prolonging, the effects of tolerance increases. Therefore, for high accuracy of stopping position, it is needed that accelerating and decelerating characteristics related to all of the aperture driving mechanism with the motor is detected in order to adjust motor control so as to respond to the effects of tolerance.
However, it is difficult to predict the characteristics of the aperture driving mechanism, including indefinite interchangeable lenses, and moreover it is nearly impossible to consider variation of load condition caused by types of lenses and difference of individual lens, and variation of electric supply condition for the motor.
Accordingly, it is an object of the present invention to provide a camera, which can drive and stop a driven member in a lens precisely.
It is another object of the present invention to provide a method for controlling an apparatus adapted to attach a unit so as to drive and stop a driven member of the unit precisely.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a camera adapted to attach a lens thereto, comprising: a lens attached part for attaching the lens thereto; a drive unit for driving a driven member in the lens attached to the lens attached part; a detector for detecting the operating characteristics of the drive unit; and a control unit for controlling the drive unit, wherein the control unit includes a preliminary drive control unit for driving the drive unit so as to drive the driven member in the lens by a predetermined amount with a predetermined timing, as a preliminary operation, and for making the detector detect the operating characteristics of the drive unit during the preliminary operation, and wherein the control unit controls the drive unit on the basis of the operating characteristics detected by the detector, as a main operation.
In the construction, depending on the operating characteristics of the drive unit detected by the detector during the preliminary operation, it is possible to grasp the influence of the variation of the loading condition in a driving system not only of a camera body but of a lens, and the influence of the variation of the power supply condition. In the main operation, it is possible to control the drive unit precisely, considering the operating characteristics detected during the preliminary operation.
Therefore, it is possible to drive and stop a driven member in a lens precisely.
As an embodiment, the control unit makes the detector detect at least one of the operating characteristics during the main operation, and the control unit controls the drive unit with reference to the at least one of the operating characteristics.
According to the embodiment, even if the characteristics of the drive unit change after the preliminary operation, it is possible to control the drive unit more precisely, considering at least one of the operating characteristics, for example, accelerating characteristic, detected during the main operation.
As another embodiment, the driven member is a member included in a mechanism for changing the size of an opening of an aperture in the lens attached to the lens attached part.
As still another embodiment, the predetermined timing corresponds to when it is detected that the lens is attached to the lens attached part.
As still another embodiment, the predetermined timing corresponds to when the electric power starts to be supplied to a camera body.
As still another embodiment, the predetermined timing corresponds to when a power switch on a camera body is switched on.
As still another embodiment, the detector detects the amount and time of operation of the drive unit, and the operating characteristics are those concerning the acceleration and deceleration of the drive unit, including a mechanical deflection and deviation.
According to another aspect of the present invention, there is provided a method for controlling an apparatus adapted to attach a unit thereto, comprising: a preliminary driving step for driving a driven member of the unit by a predetermined amount with a predetermined timing as a preliminary driving operation; a detecting step for detecting operating characteristics of a mechanism for driving the driven member during the preliminary driving operation; and a main driving step for driving the driven member as a main driving operation, on the basis of the operating characteristics detected in the detecting step.
According to the method, it is possible to drive and stop a driven member of the unit precisely.